1. Field of the Invention
The present invention is related to continuously variable transmissions. More specifically, the present invention is related to dual drive continuously variable transmissions having dual drives slaved together for transfer of torque from input shafts to output shafts.
2. Related Art
Continuously variable transmissions (xe2x80x9cCVTsxe2x80x9d) are a type of transmission capable of transferring torque from an input shaft to an output shaft. The CVT allows the speed change to occur within the transmission while the input speed is maintained at a substantially constant rotational velocity. Thus, the CVT is a transmission that is capable of converting input speeds into output speeds that are steplessly variable within a given range. Recently, these transmissions have been used in the automotive industry for transferring torque between an input shaft and an output shaft of a vehicle employing a low horsepower engine.
The most common of such CVT drives for automobiles has used a steel segmented V-belt operating with axially moveable steel pulleys that force belt radial movement along the conical pulley surfaces to change the speed ratio between the driven and the output shaft, usually by a combination of springs and hydraulic generated force. Such belts operate the drive by transferring the torque from an input shaft, through a single input pulley, to a single output pulley and, ultimately, to an output shaft. Drives of this type have been successful and, as mentioned above, are currently being commercially produced in the lower horsepower range of passenger automobiles.
Operational qualities of CVT drives are well known in the automotive industry, including their shortcomings. Continuous research and development effort is being expended in the automobile industry to extend the capabilities of the belt and pulley basic concept because of the perceived advantages to be realized over more traditional transmissions now in production.
One of the shortcomings of some current CVT drives includes limitations on operation in the higher horsepower range, the solving of which is the genesis of this invention. Thus, the present invention was designed to handle increased horsepower over single belt CVT systems. Specifically, a dual belt CVT system was created.
The creation of a dual belt CVT system, however, revealed other drawbacks. Included among these drawbacks where the complication of system construction and increased size and cost, as well as loss of the prime mover energy due to what is termed bucking of the belts against each other. The bucking of the belts occurs, for instance, when the operation of a dual drive system is not synchronous. The difficulty is further magnified when such a system must be continuously variable and automatically controlled as is required in an automotive application.
Thus, the present invention involves coupling two CVT belt systems operating in parallel. Thus, each of the CVT belt systems absorbs half the input torque of the input shaft and delivers it to the output shaft. The torque transfer occurs in the present invention with very low power loss due to an advantageously coupling of components and synchronous driving of the belt systems. Similar to some single belt systems in use, the present invention changes the pulley ratios using selective pressurization of the pulleys. Specifically, each pulley includes a biased portion that, when pressurized, alters the effective diameter of the pulley.
Because two parallel continuously variable drives, which are positioned on common shafts, may not naturally operate synchronously in the serial production world, three additional elements can be employed singularly or together to accomplish the necessary compatibility without excessive energy loss or undue complication. One such element is a device, hydraulic or mechanical, to precisely and synchronously, control the moveable halves of the drive pulleys positions to maintain an even operating radius or effective diameter of the belts on the pulleys during hydraulic pressure application for ratio changing or holding in between travel extremes. Another element is precise pulley groove width control employing accurate parts dimensions axially where the pulleys meet stops at the extremes of travel to essentially position each belt at like operating radii, or effective diameters, in both the high gear or cruise position and the low gear position, which are the positions at which the CVT will operate most of the time. The third element incorporates a differential gear set with very low friction performance. Preferably, the differential gear is installed between the two driven pulleys on the output shaft. This third element accommodates differences in output rotational speed of the output pulleys regardless of the implementation of the above-two elements. The differential therefore will accept the torque of each pulley separately even though there is a speed disparity and apply this torque to the output gear or sprocket, through the so-called spider gears of the differential, with minimal energy loss.
Accordingly, it is an object of this invention to provide a CVT system in a compact arrangement. The system should be capable of handling increased horsepower and should be mechanically producible using conventional materials and processes at reasonable cost. The present invention, therefore, has been engineered in a generic form that may be readily tailored to a specific application. However, it is envisioned that the present invention will have particular utility in the automotive industry, for example.
A dual belt and pulley system arranged and configured in accordance with the present invention can easily be understood by one familiar with the much used single system. It can be seen that the present system, incorporating a unique, compact mechanical arrangement of the elements necessary to ensure the compatibility of side-by-side operation very simply makes possible the doubling of the torque capacity of any such single system. The use of this practical concept today does not require xe2x80x9cstate of the artxe2x80x9d development of the single belt and pulley design per se but whatever such advances may come to pass in the future, their capability can also be doubled. It should also be noted that the drive shaft, as explained herein, can become the driven shaft without modifications other than installation considerations of packaging.
One aspect of the present invention involves a continuously variable transmission comprising an input shaft. The input shaft supporting two input pulleys and the two input pulleys each comprising a fixed disk portion and a moveable disk portion. Axial movement of the moveable disk portion along the input shaft relative to the fixed disk portion changes an effective diameter of the pulley. The moveable disk portions of the two input pulleys are interposed along the input shaft between the fixed disk portions of the two input pulleys and a synchronizing member connects the two moveable disk portions such that the effective diameters of the two input pulleys are maintained as substantially equal by the synchronizing member.
Another aspect of the present invention involves a continuously variable transmission. The transmission comprises a first belt assembly and second belt assembly that extend between a torque transmitting shaft and a torque receiving shaft. The first belt assembly comprises a first drive pulley, a first driven pulley and a first belt while the second belt assembly comprises a second drive pulley, a second driven pulley and a second belt. The first drive pulley and the second drive pulley each comprise a moveable drive sheave portion and a fixed drive sheave portion. The moveable drive sheave portions are capable of movement along an axis of the torque transmitting shaft. The first driven pulley and the second driven pulley each comprise a fixed driven sheave portion and a moveable driven sheave portion. The moveable driven sheave portion is capable of movement along an axis of the torque receiving shaft. The moveable drive sheave portions are connected by a mechanical linkage to equalize the movement along the axis of the torque transmitting shaft between the first drive pulley and the second drive pulley. A differential connects the fixed driven sheave portions to the torque receiving shaft.
Another aspect of the present invention involves an axially expandable pulley arrangement comprising a first pulley disk and a second pulley disk. The first disk comprises a first front face, a first back face and a first hub while the second disk comprises a second front face, a second back face and a second hub. The second hub extends at least partially within the first hub and the first back face includes a circumferential flange. A piston is positioned within the flange and is slidably connected to the first back face. The piston also is connected to the second hub through an aperture defined in the first hub such that movement of the piston relative to the first pulley disk results in corresponding movement of the second pulley disk relative to the first pulley disk.